That would be too long, it's faster that you compile giac with
CXXFLAGS=-g,
run gdb on icas and make a breakpoint in pari.cc, line 426.
Then for example
(gdb) r 'pari("sin",x)'
will stop just before flisexpr is called
The call comes (f 1) from the _pari function, and you will see
at line 556 that I replace PARI_stack_limit by 0

I'm sorry, it's more complex than just running the icas text version,
since it does not call pari inside a new thread. You must compile
xcas, run it (instead of icas) in gdb, same breakpoint
and do r in gdb, then enter pari("sin",x) in a commandline
and valid to see the call in a separate thread.